This invention relates to a process for producing a particulate polymer having imide groups, and more particularly to a process for producing a particulate polymer having imide groups which is excellent in heat resistance and usable mainly as sheet, molded article, adhesive, coating material, composite material and the like.
There is known a technique for producing a solution of polymer having imide groups, such as polyamide-imide solution, polyimide solution and the like, by reacting a polyisocyanate with a polycarboxylic acid having acid anhydride group in the state of a solution in expensive solvent such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide or the like. However, in order to obtain a solid polymer from such a polymer solution, the solvent must be removed or recovered by a quite ineconomical process, so that production of polymer by such a process has an important problem in point of cost if it is practised on an industrial scale. One of the useful processes for producing solid polymers is bulk polymerization process necessitating no use of solvent. However, polymers having imide groups generally have a rigid and highly polar molecular structure and are characterized by having a high glass transition temperature. Accordingly, in applying bulk polymerization process to their production, the reaction must be carried out under serious conditions such as high temperatures and high pressures, which makes it difficult to control the reaction and to suppress side reactions. Thus, no successful result has ever been reported in its practical application.